Monday, December 24, 2012

Global Warming on West Antarctic Ice Sheet three times the global average


The West Antarctic Ice Sheet is warming at three times the global average, according to temperature measurements at Byrd Polar Station. This has implications for the melting of the West Antarctic Ice sheet (WAIS) and sea level rise.


The West Antarctic Ice Sheet is inherently unstable due to it's grounding in a deep depression below sea level. Warm Southern ocean currents are already reducing ice shelves holding back ice discharge from glaciers. As these ice shelves are undermined and break up it will allow significant acceleration of glacier discharge increasing the rate of sea level rise.

Lead study author David H. Bromwich from Ohio State University said:

"Our record suggests that continued summer warming in West Antarctica could upset the surface mass balance of the ice sheet, so that the region could make an even bigger contribution to sea level rise than it already does," said Bromwich.

"Even without generating significant mass loss directly, surface melting on the WAIS could contribute to sea level indirectly, by weakening the West Antarctic ice shelves that restrain the region's natural ice flow into the ocean."

Related: Global warming in Antarctica: Thwaites and Pine Island Glaciers | Waking the giant: Global Warming in the Weddell Sea | Southern Ocean warming impact on Antarctic Ice Sheet and global sea level

This new study published in Nature Geoscience - Central West Antarctica among the most rapidly warming regions on Earth - shows that a significant warming trend over the last 50 years has been occurring at the top of the ice sheet at Byrd Polar Station. The study confirms an earlier study by Steig et al published in 2009 in Nature: Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year which was met with some degree of scientific scepticism. According to Eric Steig writing on Real Climate Blog: The heat is on in West Antarctica -

"they do more than back-up our results: they show that our estimates were too conservative and that West Antarctica is actually warming by about a factor of two more than we estimated. They also agree with the key interpretation of the results that both we and David Schneider and colleagues at NCAR have presented: that in the winter and spring seasons, when the most rapid warming is occurring in West Antarctica, the driver has been changes in the tropical Pacific, not the ozone hole (which is invoked too frequently, in my view, to explain everything from penguin populations to sea ice changes)."


Increasing Sea Surface temperatures in tropical pacific impacting West Antarctica

A 2011 paper in Nature Geoscience - Winter warming in West Antarctica caused by central tropical Pacific warming (abstract) - details how sea surface temperatures in the tropical pacific are contributing to the widespread warming trend in West Antarctica:

"recent warming in continental West Antarctica is linked to sea surface temperature changes in the tropical Pacific. Over the past 30 years, anomalous sea surface temperatures in the central tropical Pacific have generated an atmospheric Rossby wave response that influences atmospheric circulation over the Amundsen Sea, causing increased advection of warm air to the Antarctic continent. General circulation model experiments show that the central tropical Pacific is a critical region for producing the observed high latitude response. We conclude that, by affecting the atmospheric circulation at high southern latitudes, increasing tropical sea surface temperatures may account for West Antarctic warming through most of the twentieth century."

Most polar research stations are scattered around the edges of Antarctica, with a couple located in central East Antarctica including the US South Pole base. Byrd Polar Station is unusual in being the only place measuring changes in the centre of West Antarctica. For most of the time the base is unpopulated taking automated measurements.

Study co-author Andrew Monaghan from the National Center for Atmospheric Research (NCAR) said that this now places West Antarctica as one of the fastest arming regions on the planet.


"We've already seen enhanced surface melting contribute to the breakup of the Antarctic's Larsen B Ice Shelf, where glaciers at the edge discharged massive sections of ice into the ocean that contributed to sea level rise," Monaghan said. "The stakes would be much higher if a similar event occurred to an ice shelf restraining one of the enormous WAIS glaciers."

It is estimated that the West Antarctic ice sheet currently contributes 0.3 mm to sea level rise each year. behind Greenland's present contribution of 0.7 mm per year.

The Byrd Polar Research station was established in 1957, but was not constantly populated. An automated weather station as installed in 1980, but experienced power outages through the long polar winter due to it's reliance on solar panels recharging the batteries powering the station. Up to a third of the temperature record as missing due to these problems. The researchers had to use corrected data from a computer atmospheric model and a numerical analysis method to fill in the missing observations.

The temperature analysis offers a more complete picture of warming in West Antarctica. Bromwich said the results show more observations are needed in the region.

"West Antarctica is one of the most rapidly changing regions on Earth, but it is also one of the least known," he said. "Our study underscores the need for a reliable network of meteorological observations throughout West Antarctica, so that we can know what is happening--and why--with more certainty."

Ice Sheet Melting is Non-linear, multi-metre sea level rise possible

So now the Arctic, Antarctic Peninsula and West Antarctica are showing strong trends of global warming. This does not bode well for the Greenland and West Antarctic Ice sheets, and will probably result in their dissolution.

But a drastic reduction in CO2 emissions we may yet control the rate of dissolution and the rate of sea level rise. Dissolution and melting of ice sheets is a non-linear response to global warming, and may occurr at a rapidly accelerating pace. This article on Climate State website says sea level rise of 1 to 3 metres (or more) within the next 50 years is possible. This article quotes as one of it's sources Hansen et al. from a 2011 Andrew Glickson paper - Climate change: a warning from the past
(PDF):

"... amplifying feedbacks make ice sheet disintegration necessarily highly non-linear. In a non-linear problem, the most relevant number for projecting sea level rise is the doubling time for the rate of mass loss. Hansen (2007) suggested that a 10-year doubling time was plausible, pointing out that such a doubling time from a base of 1 mm per year ice sheet contribution to sea level in the decade 2005-2015 would lead to a cumulative 5 m sea level rise by 2095."

Sources

  • Eurekalert - Media Release from Ohio State University, 23 December 2012 - Study shows rapid warming on the West Antarctic Ice Sheet
  • David H. Bromwich, Julien P. Nicolas, Andrew J. Monaghan, Matthew A. Lazzara, Linda M. Keller, George A. Weidner, & Aaron B. Wilson, Central West Antarctica among the most rapidly warming regions on Earth (abstract) , Nature Geoscience (2012) doi:10.1038/ngeo1671
  • Eric Steig, Real Climate, 23 December 2012, The heat is on in West Antarctica
  • Steig, E.J., Schneider, D.P. Rutherford, S.D., Mann, M.E., Comiso, J.C., Shindell, D.T. Warming of the Antarctic ice-sheet surface since the 1957 International Geophysical Year, Nature 457, 459-462, doi:10.1038/nature07669 (2009).
  • Image Caption: Researchers at Ohio State University and their colleagues have discovered that the central region of the West Antarctic Ice Sheet (WAIS) is experiencing twice as much warming as previously thought. Their analysis of the temperature record from Byrd Station (indicated by a star) sheds some light on temperature changes over a broad portion of the WAIS. This site provides the only long-term temperature observations in the region, far away from the permanent research stations with long-term temperature records (indicated by black circles) that are scattered around the continent -- making a case, the researchers say, for a more robust network of meteorological observations on the WAIS. On this map, the color intensity indicates areas around Antarctica that are likely experiencing comparable warming to Byrd Station. Credit: Image by Julien Nicolas, courtesy of Ohio State University.